1. Field of the Invention
The present invention relates to a deflection correcting method for a robot, in which the deviation between commanded and actual endpoint positions caused by deflection of the robot is determined, and command values for individual axes are corrected on the basis of thus determined deviation, whereby the robot endpoint position is controlled to a desired position.
2. Description of the Related Art
Recently, robots have been utilized in various industrial fields, and there is an increasing demand for higher accuracy of the robot.
However, the robot endpoint position or robot hand position tends to be displaced due to the presence of deflection caused by robot's own weight and load on the endpoint, backlash in a reduction gear, or the like. In the case of a teaching/playback method, however, no such problem will be encountered because the robot can be played back to a taught position and configuration. More particularly, when teaching a position and orientation to the robot, the teaching is made including the displacement of the endpoint position caused by the above deflection, backlash, or the like, so that the robot can be exactly controlled to the thus taught position and configuration during the playback operation of the robot. However, in case that a robot is operated in accordance with an operation program prepared off-line without using the robot, to which the program is to be applied actually, the deviation occurs between the robot endpoint position commanded by the operation program and the actual robot endpoint position due to the aforementioned deflection, backlash or the like, thereby causing the endpoint position displacement. When the endpoint position is displaced, the robot cannot recognize its own accurate endpoint position, and therefore, positional accuracy of the robot will be affected adversely. Thus, the displacement of the robot endpoint position caused by such deflection, etc. must be corrected in a suitable manner compared with a command value.
Conventionally known as a correcting method is a method for correcting the displacement in accordance with load acting on the endpoint, for instance. However, according to this correcting method in which the configuration of a robot is not considered, merely a fixed amount of correction is provided irrespective of the configuration of the robot. Therefore, depending on the robot configuration, an appropriate correction value cannot be provided, thereby resulting in a failure in achieving accurate correction.
Also known is a method in which the displacement of a link is determined using an analytical technique based on strength of materials or a finite-element method to correct the displacement of the endpoint. However, this method is not only time-consuming but also costly in calculating the displacement.
The conventional correcting methods have such problems, and thus it is difficult to have a robot recognize the accurate position of its endpoint which actually in a deflected state.